Animal foragers



Which forager type would typically get the best balance of nutrients from their food?

Carnivore foraging


  • Carnivore prey items contain essentially the same mix of nutrients
    • unlike herbivore and omnivores
  • Foraging success is assumed to be limited by prey availability (quantity)
    • Rather than nutritional balance (quality).

Carnivore Foraging: Quanitity vs Quality


  • Food quantity driving consumption rates, and thus predator-prey populations, is often challenged
    • Lotka Voltera vs Optimal Foraging

Case study #1: Wolf spiders, prey quality and consumption


  • Wolf spider feeds near standing water in California (Greenstone 1979)
    • 80% of the diet is shore flies, water boatmen and mosquitoes


  • Prey species were marked as either present or absent in each spider gut
    • spiders classified into groups (answer Q1)





  • Spider stomach contents (total N = 1226) from 13 different pools of water



  • Spiders from 7 out of 13 pools were more likley than by chance to have consumed all 3 prey
    • polyphagy


  • Side note: Can you imagine making graphs without modern computers!!!

Leveling up with Mayntz et al. 2005



  • Hypothesis: IF wolf spiders optimize nutrient intake, THEN they should choose a prey type that remedies a prior nutritional deficiency
    • experiment manipulating findings from Greenwood (1979)


  • Nutritional state of the Wolf spiders manipulated by feeding them a pre-treatment diet
    • fruit flies with high or low ratio of protein to lipid for 1-2 days.


  • Then tested feeding responses to the pre-treatment food and/or a complementary alternative
    • offered only 1 choice (same or different prey)
    • recorded how much of each was eaten
    • Answer Question 3

Leveling up with Mayntz et al. 2005 (answer Questsion 4)


Today Quantitative Reasoning Practice




  • In your groups, work through interpretation of the results from these papers


  • Use your knowledge of species interactions and evolution to theorize about more complex predator-prey relationships


  • These are great practice exam questions!!!